Electronegativity + Intermolecular Interactions + Periodicity Flashcards
Electronegativity
The ability of an atom to attract the bonding pair of electrons towards itself in a covalent bond
Pauling electronegativity values
Used to compare the electronegativity of the atoms of different elements. By these values, the atom with the larger value is δ-
What is the most electronegative element
Fluorine
Key electronegative elements
N
O
F
Cl
Br
Electronegativity across a period ➡️
Increases ⬆️
Electronegativity down a group ⬇️
Decreases ⬇️
δ meaning
Slightly
Dipole bond when…
There is a great enough difference between electronegativity of atoms.
A dipole is the separation of partial charges in a molecule.
The separation of partial charges across a polar bond, arising
Symmetrical molecules with Polar bonds
Permanent dipoles cancel out resulting in non-polar molecule (despite individual bond dipoles) (poalr if e- shared unequally)
Symmetrical if…
NO lone pairs
All same bond type
Asymmetrical if…
Has lone pairs
Different bond types present
Intermolecular
Between molecules
Instantaneous dipole
Where the bonded electron pair is shared unequally between the bonded atoms
Induced dipole
A dipole formed due to it being next to an instantaneous dipole
Induced dipole dipole interactions (London/Dispersion forces)
Weak intermolecular forces that exist between all molecules (polar or NP)
Permanent dipole dipole interactions
Weak intermolecular forces that exist between the permanent dipoles in different polar molecules
Van der Waals
Used to describe both induced dipole dipole and permanent dipole dipole intermolecular forces
Hydrogen bonds
Type of permanent dipole dipole interaction found between molecules containing an electronegative atom with a lone pair of electrons (N, O or F) and a hydrogen attached to an electronegative atom in another molecule
How does an induced dispose dipole interaction form
- e- randomly move to 1 side of atom -> uneven distribution -> dipole
- Dipole repels e- in next molecule -> dipole
- Electrostatic attraction between + and - dipoles -> induced dipole dipole interaction
- Temporary - force will disappear, return to non polar molecules
All intermolecular forces are based on
Small electrostatic attraction between atoms which have been polarised in adjacent molecules
Impact of number of e- on induced dipole dipole attraction
More e- = more energy to break intermolecular force = higher BP
How are intermolecular forces measured
MP/BP
(Easily measured)
Effect of molecule shape on induced dipole dipole interactions
Less branched = more points of contact between molecules = stronger induced dipole dipole interactions
Molecules with permanent dipole dipole interactions also have…
Induced dipole dipole - these are present between ALL molecules
So more energy to overcome both rather than just induced
